1. Technical Field
This invention relates generally to data communication between stages of photographic filmstrip use and processing wherein data is recorded in a magnetic layer of the photographic filmstrip at a first stage and read out at a second stage. More particularly, the invention relates to a method and apparatus for enhancing the reliability of such data transfer.
1. Background Information
Data communication between different stages of film use and processing (e.g. a camera user and dealer or photofinisher) has traditionally required separate written forms. This has not proven to be a very convenient or efficient method of relaying important information from one stage to another.
In the early 1960's, an innovation in data communication for motion picture film was introduced. A thin layer of magnetic oxide, referred to as a DATAKODE Magnetic Control Surface, was coated across the entire back surface of a roll of motion picture film to provide the capability to magnetically record digital data on the film without interfering with normal photographic use of the film.
The DATAKODE Magnetic Control Surface permitted recording of different types of digital data at different stages of production of a motion picture. Such data could range from camera, lighting and filter data at the time of shooting to printer exposure control information in the laboratory to theatre automation control signals during exhibition. The availability of the DATAKODE Magnetic Control Surface over the entire surface of the motion picture film allowed multiple types of data to be recorded on the same piece of film.
The DATAKODE Magnetic Control Surface was specifically applied to the recording of SMPTE time and control code on motion picture films. In implementing this technology head-to-film contact was recognized as one of the most important factors in getting good quality time-code signal recordings. Both recording heads and playback heads needed to be mounted in a manner that maintained intimate and stable contact between the film and the gap of the magnetic head.
More recently, a film information exchange system using dedicated magnetic tracks has been developed for use in still photography. A virtually transparent magnetic layer on the still photography filmstrip facilitates the magnetic recording of data in one or more longitudinal tracks of each film frame. With a virtually transparent magnetic layer, data recording may be done everywhere on the filmstrip including in the image area, so that all relevant information can theoretically be recorded with each frame on the film. U.S. Pat. No. 4,965,627 issued Oct. 23, 1990 describes such a system, the disclosure of which is incorporated by reference herein. In order to provide quick access to particular data at any stage of film use, related data is preferably grouped and recorded in specific predetermined tracks. Camera data is recorded in several dedicated longitudinal tracks located along the filmstrip edges. The camera data, as well as other data, is preferably recorded in pulse position encoded form in order to be independent of film transport velocity. Other new features and advantages of the Film Information Exchange System Using Dedicated Magnetic Tracks are described in U.S. Pat. No. 4,965,627 and the related patents referenced therein.
As in the earlier DATACODE Magnetic Control Surface application, the Film Information Exchange System Using Dedicated Magnetic Tracks of U.S. Pat. No. 4,965,627 requires a high quality head-to-film interface (HFI) over the entire write/read cycle in order to ensure that a complete set of data is transferred between different stages of film processing and use. In implementing this system in a camera, for example, a load pad is needed for high quality HFI. Due to the required load force, the load pad must be unloaded from the film when magnetics is not in use, in order to prevent dimpling of the film and out-of-flat negatives that might risk the photographic quality. Such an unload mechanism adds cost and complexity to the camera.
Also, to deliver a full set of camera data, it is desirable to employ an edge guided magnetic recording subsystem in the camera. This subsystem may need to be unloaded when magnetics is not in use for the same reason as the load pad again increasing the cost and complexity of the camera. Accordingly, implementation of a read/write magnetics subsystem in a camera can pose a significant cost problem, particularly for relatively inexpensive cameras.
To eliminate the need for a camera load pad which has to be unloaded from the film when not in use, a relatively simple and inexpensive constant contact load pad might be devised. However, such a simple constant contact load pad may not be sufficient to maintain a quality head-to-film interface throughout an entire film frame, thereby potentially compromising the reliability of data transfer.
In the earlier applications of a virtually transparent magnetic surface to motion picture and still photography filmstrips, a 1:1 relationship between the number of recording heads and playback heads was employed. The paired recording head and playback head were of the same width or, as shown in FIG. 4 of U.S. Pat. No. 4,965,627, the width of the playback head could be made smaller than that of the recording head in order to accommodate lateral meandering of the recorded track.
In other environments, various approaches have been developed for centering a readback head relative to a magnetic track. U.S. Reissue Pat. RE. 31,166 describes a system for reading a relatively wide magnetically recorded track with a relatively narrow read head located at the approximate center of the track. Illegible information recorded along the track is recovered by moving the read head transverse to the track length from a normal position to a new track position.
Instead of mechanically positioning a playback head, various approaches for electronically selecting appropriate head(s) centered over a magnetic track have been suggested. U.S. Pat. No. 3,769,465 describes a high density recording system which employs a plurality of fixedly positioned playback heads to read information from each of several adjacent tracks on a magnetic recording surface. Electronic gating is used to select the transducer(s) presently centered over a track to be read out. A first plurality of transducers monitor a guard band on the magnetic recording surface. These transducers detect the lateral edge of recorded information. The tracks on the magnetic surface are in a fixed position relative to this lateral edge. Detection of the lateral edge thus permits the electronic selection of transducers which will be centered over each track on the recording surface. In one embodiment of this earlier patented system a centered pair of adjacent transducers is electronically selected for each track and the outputs of the pair of transducers are summed.
Another approach for electronically selecting read back heads centered over a magnetic track is described in U.S. Pat. No. 4,616,272. This patent describes a digital signal reproducing apparatus for reading data from a magnetic tape having n tracks. A guard band separates each pair of adjacent tracks. The reproducing apparatus includes n reproducing element groups provided in correspondence with the n tracks. Each of the reproducing element groups includes a plurality of reproducing elements arranged in the tape width direction over a range of a corresponding track and guard bands on both sides thereof. The reproducing elements of a group monitor the magnetic field intensity distribution. Outputs of those reproducing elements opposing a uniform part of the magnetic field intensity distribution are selectively added to produce a combined output for a track.
The electronic servo approaches of U.S. Pat. Nos. 3,769,465 and 4,616,272 rely on the existence of guard band(s) in predetermined relationship to the magnetic tracks and assume a good head-to-film interface at the recording and playback heads. Both of these techniques are directed towards electronic selection of playback heads which are physically centered with regard to a track and sum the outputs of such heads to produce an output signal. Neither of these patents recognize, address or resolve the problems associated with data transfer via magnetic recording on a photographic filmstrip, especially when good HFI is not guaranteed.
In addition to cost and HFI considerations, the application of magnetics on photographic film to transfer data raises other unique concerns. For instance, the filmstrip which serves as the magnetic recording medium may experience jitter caused by the film transport mechanism, spacing losses due for example to dimples in the film or to dirt, and track wander if the film is laterally displaced relative to the recording head during the recording process. Such physical disturbances can result in the introduction of corruption errors in the transferred data.
A need therefore exists for a technique for ensuring the reliable transfer of data via magnetic recording on a photographic filmstrip when persistent high quality HFI cannot be guaranteed and when the data transfer is subject to such corruption errors.